While hot seating a friend, I noticed that she button-spams while grappling a Survivor. It doesn't change the Special Infected animation at all but she swears that it does more damage. In particular she thinks the Jockey is still able to attack while riding. I'm inclined to think that the game inflicts maximal damage regardless of what you're doing once your SI has started to grapple.
So what's the real story?
Does button spamming increase the damage dealt by a special infected?
Note: Grappling Special Infected